Process for preparing acrylonitrile fibers



R. D. EU LER March 14, 1961 PROCESS FOR PREPARING ACRYLONITRILE FIBERSFiled May 20, 1958 FIG. 3

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@QQQQQQQQQQQQ ATTORNEY 2,975,022 PROCESS non PREPARING ACRYLONITRILEThis invention relates to the preparation of acrylonitrile fibers ofmodified cross-sectional shape. More particularly, this inventionrelates to a process for preparing fibers of a uniform,-roundcross-sectionalshape from copolymers of acrylonitrile by adry-spinningprocess.

Fibers arereadily prepared from acrylonitrile polymers by dissolving thepolymer in -.a suitable organic solvent such-as dimethylforr'namide-andextruding the resultant solution into an evaporativeatmosphere. I Tlhepolymer used may be a homopolymer of acrylonitrile-or 'a copolymer ofacrylonitrile containing up to 15% of one or more additionalcopolymerizable monomers to improve dye depth and dye uniformity, ortointroduee other desirable properties in the final yarnr;

Acrylonitrile fibers prepared by jknownprocesses have distinctivecross-sectional shape. -The cross-sections are in the form of dog-honeso r dumbbells. While filaments of this shape are suitable for manypurposes, they are easily. bent in the direct-ion of the short axis ofthe cross-section. If increased stiffness is desired in such a filament,it is necessaryto increase thecross-sectional area.

.It is, therefore, an object of invention to provide a, processforpreparing fibers from acrylonitrile copolymersmwhich donot have adog-bone or'dumbbell crosssectionaLshape. 'It is a further object oftheinvention to produce acrylonitrile copolymer fibers having a uniform,round cross-sectional shape. Additional objects will appear hereinafter.

fl}hese:and other objects of the invention are accomplishedby extrudinga solution of a polymer containing at least 85% acrylonitrile in avolatile organic solvent at awtemper'ature from about 130 C. to about145 C. through-an orifice into a spinning cell which isfdivided intotwo-zones, the first zone containing an essentially static gaseousmedium which issubstantially'saturated with a solvent for the polymerand is heated to a temperature from about 165 C. to about 205 C1, andthe second zone-containing a gaseous mediumessentially free from solventwhich is heated to a temperature'from about 50C.-to about 100 C. Theflow of the gaseous medium in the second zone may be co-current orconcurrent with the'direction of travel of the filaments. The filamentsare removed from the spinning cell ata ratefro'm about 27540350 yardsper minute. 7

The present invention will be more clearly understood by reference tothe accompanyingdrawingsin which Figure l is a representative'drawingoftheoross-sectional shape of a bundle of fibers of the present invention;Figure Z-i-llustrates the cross-sectionalshape of the filaments preparedby known prior art processes; and Figure 3 is a side elevation, partlyin cross-section, of suitable apparatus for practicing this invention, 1j

\ Referring to the drawings, in Figure 3 a solution of polymer ismetered under pressure through inlet 1 to spinneret 2 which contains aplurality of small orifices, riotshown, to form filaments 3. As thefilaments enter spinning cell 4; they pass into solvent-laden, jacketedUn ed 5% Patent 9 zone I. Suitable ba'fiiing, not shown, may bepositioned which are relatively wet with solvent pass through zone- Iinto zone II of spinning cell 4 which is unheated where they aresurrounded by a countercurrent flow of. an essentially solvent-freegaseous medium which is introduced through inlet 6 andremoved throughoutlet 7. The substantially dry'rfilaments are then converged near exit8, passed out of the spinning cell, over guide roller 9', and then to asuitable collecting device not shown.

The apparatus shown in Figure 3 may, of course, be modified to includemeans for initially introducing a solvent laden' gaseous medium intozone I; however, aftertheprocs's is in operation, it has been found thatthe solvent removed from the spinning solution as the filamentscoagulate is suflicient to maintain "a substantially solvent-saturatedatmosphere. It has been found desirable to maintain fa'fsifiallneg'ative static pressure, e.g.-, in the order of "-0.l5 inch of water,throughout the spinning cell to prevent objectionable condensation ofsolvent 'nearexit'fl. V

The production or uniformly round a'crylonitrile fila ments is onlypossible by maintaining a "critical combination of con'ditions Withinthespin'ning apparatus. The 5. temperature of the spinning solution mustbe'be't ween about 130 C. and 145 C. it the temperature falls'b'elovvthe lower limit, the filaments tend to' coalesce and stick together. 'Ifthe temperature goes above 145 C., the

dog-bone shaped'structures of" the zpxior'art are first o btained andthen bubbles appear. The temperature of z lie I of the spinning cellmust be maintainedbetween about 165 C. and 205 C. If th'etemperaturefalls'b elow-165 C.,the filaments stick together, and if itrises above 205 C., dog-bone shaped'filam'ents are obtained. Theterriperature of the' gaseous medium which is introduced into zone II ofthe spinning cell rnustals'o be closely regulated.- At temperaturesbelow about 5 0 "C.-, "the filaments coalesce and, at temperatures aboveC., the convert I tional d0g-bone shaped filaments are produced. Thefil'aments must be removed at a rate of about 275, yards'per minute toprevent theformation of the dog-bone crosssectional shapes; however, therate must not exceed about 350 yards per minute or the filaments"again'coalesce.

The invention will befurther illustrated but'is not inf tended to belimited by the following examples in which parts and percentages aregiven by weight unless other- 5 wise specified.

Example I p a A spinning solution was prepared by dissolving partsofa-copolymer containing 94.0%acrylonitrileand I 6.0% methyl acrylate in69'pa1ts'of dimethylformamide."

The viscosity of thissolution, as measured at JC;

was 52 poises. Apparatus similar to that shown in'Figure f a 3 was usedin spinning the 'solutionintofilaments The solution was heated to andwas forced' ati-th'e" rate of 38.8 grams per minute througha spinneret'hav ing 30 orifices 0.11 millimeter in diameter into a spin ning cell 8inches in diameter and'16 feet long. Keinp gas, essentially a mixture ofabout 87% nitrogen and 13% carbon dioxide, was heated to a temperatureof60 C. and passed into a zone at the bottom'of 'tlie s'piii ning cellthrough an inlet-located at a point about '5 inches from the exitpoint'for the yarn. This aspiration gas was removed from the cell at'a'point about tfeet above the point of entrance. The zone at:the,bottornidf' the spinning cell was unheated except for the heating ef-=fect of the Kemp gas. The 12-foot z onepf spinning jcell between thespinneret and thepoint at which tion gas was removed-was heatedto atempe tur 2,975,022 I Patented Mar. 14,

180 C. This zone contained no openings for introduction of removal ofaspiration gas. The yarn collected from the spinning cell was treatedwith an aqueous finish and was then wound onto a bobbin at a speed of300 yards per minute. This yarn was found to contain 39.8% solvent.After removal of this solvent, the yarn was found to have a denier of395. The filaments were found to be uniformly round in cross-sectionalshape.

Bobbins of the spun yarn were extracted with water and dilute aqueoussolutions of dimethylformamide at temperatures between 25 C. and 100 C.The resultant extracted yarns were then drawn to from 4 to 8 times theiroriginal length and were then relaxed 10% to The final relaxed yarnswere all found to have the same cross-sectional shapes as the spun yarn.

Example II Example I was repeated except that the spinning solution wasa terpolymer containing 93.7% acrylonitrile, 6.0% methyl acrylate, and0.3% styrenesulfonic acid, and a spinneret having triangular holesmeasuring 0.18 millimeter on an edge was used. In spite of the shape ofthe spinneret holes, the filaments obtained were perfectly round asshown in Figure 1. This experiment demonstrates that it is the criticalselection of spinning conditions and not the shape of the orifice whichcontrols the shape of the filaments formed.

The process of this invention is not limited to the preparation offilaments from the copolymers specified in the examples but is equallyapplicable to producing round filaments from other copolymers ofacrylonitrile containing at least 85% combined acrylonitrile in thepolymer molecules. The polymer may contain from 2% to 15% of one or moreethylenically unsaturated monomers which are copolymerizable withacrylonitrile. For example, any of the monomers mentioned in U.S.2,436,926 or U.S. 2,743,994 such as acrylic methacrylic, andalphachloracrylic acids, methyl methacrylate, ethyl methacrylate, butylmethacrylate, octyl methacrylate, 2-nitro-2- methyl propyl methacrylate,methoxyethyl methacrylate, chloroethyl methacrylate, phenylmethacrylate, cyclohexyl methacrylate, dimethyl aminoethyl methacrylate,and the corresponding esters of acrylic or alpha-chloro acrylic acids;acryland methacryl-arnides or monoalkyl substitution products thereof;unsaturated ketones such as methyl vinyl ketone, phenyl vinyl ketone,and methyl isopropenyl ketone, vinylidene chloride, vinyl chloride,vinyl fluoride, vinyl carboxylates such as vinyl acetate, vinylchloroacetate, vinyl propionate, vinyl butyrate, vinyl benzoate, vinylthiolacetate, and vinyl stearate, ethylenealpha, beta-dicarboxylicacids, or their anhydrides or derivatives such as maleic anhydride,fumaric, maleic, citraconic, and mesaconie esters, N-alkyl maleimides;N- vinyl carbazole, N-vinyl succinimide, N-vinyl phthalimide, vinylcthers, monoolefins, or substitution products thereof such as styrene,furyl ethylene, ethylene, and isobutylene may be used. In addition, thecopolymers may contain from about 0.1% to about 10% of a copolymerizablemonomer having sulfonic acid or sulfonate salt groups such asallyloxyethylsulfonic acid, allylthiopropanolsulfonic acid,vinyldichlorobenzenesulfonic acid, naphthylethylene sulfonic acid,methyl styrenesulfonic acid, as well as disulfonic and amino sulfonicacids.

The concentration of the polymer in the spinning solution should bebetween about 25% and 40%, and the solution should have a viscositywithin the range of about 15 to 750 poises at the temperature ofspinning with viscosities between about 50 and about 200 poises beingpreferred. The gaseous medium may be selected from any of a number ofsubstantially inert compositions, e.g., Kemp gas, nitrogen, carbondioxide, etc., as well as air may be used.

The various temperatures and flow conditions involved in the spinningwill depend somewhat on the polymer being spun, the concentration ofsolution of that polymer in solvent, and the spinning speed being used.nowever, the solution temperature, the temperature in zones I and H ofthe spinning cell, the inlet gas temperature, and the spinning speedmust be maintained within the critical limits previously set forth. Therate of flow of the gaseous medium introduced into zone 11 of thespinning cell should be from about 20 to about 60 pounds per hour. Theflow is countercurrent to the direction of travel of the filaments. Iprefer to use a solution temperature of 133 C. to 137 C. with atemperature of 170 C. to 200 C. in zone I and an inlet gas temperatureof 55 C. to 70 C. in zone II, and to adjust the rate of aspirationwithin the range previously described to give a level of good spinningcontinuity and good yarn uniformity, according to the polymer andsolution concentration employed.

The apparatus used in practicing the invention may be similar to thatshown in Figure 3; however, many modifications as well as other suitableapparatus will be apparent to those skilled in the art. For example, thespinning apparatus described in U.S. 2,615,198 with certainmodifications would be acceptable. A- spinneret of the type described inU.S. 1,883,423 is preferred.

The length of the zones in the spinning cell which is heated and thelength which is unheated are not critical; however, I prefer to use aheated section from about eight to sixteen feet in length and a lowerunheated section from about four to eight feet in length. It is notessential that the point of removal of the aspiration gas be immediatelyadjacent the lower end of the heated section of the cell. The gasmay beremoved at a point several feet above or below the line of separation ofthe heated and unheated sections. However, steps must be taken tomaintain the solvent-laden atmosphere and critical temperature range inthe upper section. The gas is preferably removed at a point in the lowersection of the spinning cell.

The products prepared by the process of this invention are particularlyuseful in the preparation of woven, knit, and pile fabrics for use inthe apparel trade. The fabrics prepared from such fibers have improvedcrispness of hand without increasing the individual filament denierwhich would result, in some cases, in an over-all coarseness of fabricquality. Where the fibers are used in staple form and must be convertedfrom staple to yarn by such spinning systems as the cotton system orwoolen system, the fibers so prepared permit improve ments in handwithout altering the fineness of the yarn count that may be spun. Afurther advantage of the fibers of my invention lies in the fact thatfabrics prepared from these fibers do not show an undesirable shinysurface, which is frequently true of fabrics made from dogbone shapedfilaments because of the tendency of those filaments to arrangethemselves parallel to the surface of the fabric itself.

The chief advantage of the process of my invention is that it allows thepreparation of filaments having a uniformly round cross-sectional shapefrom copolymers of acrylonitrile by a dry-spinning process whichheretofore has not been possible. In addition, the process does notrequire complicated equipment and may be practiced using existingequipment with only minor changes being required.

It will be apparent that many widely different embodiments of thisinvention may be made without departing [from the spirit and scopethereof, and therefore it is not intended to be limited except asindicated in the appended claims.

' I claim:

, 1. A process for preparing acrylonitrile filaments having a uniform,round cross-sectional shape which comprises extruding a solutioncontaining a polymer comprised of at least acrylonitrile and up to about15% of an ethylenically unsaturated monomer copolymerizable withacrylonitrile in dimethylformamide at a temperature from about 130 C. toabout 145 C. through a spinneret into an atmosphere containing asubstantially solventsaturated static gaseous medium heated to atemperature from about 165 C. to about 205 C., and thereafter passingsaid filaments through an atmosphere containing a substantiallysolvent-free gaseous medium heated to a temperature from about 50 C. toabout 100 C. and withdrawing said filaments at a rate from about 275 toabout 350 yards per minute.

2. The process of claim 1 wherein said solution is at a temperature fromabout 133 C. to about 137 C., said solvent-saturated gaseous medium isat a temperature from about 170 C. to about 200 C. and said solventfreegaseous medium is at a temperature from about 55 C. to about 70 C.

3. A process for preparing acrylonitrile filaments having a uniform,round cross-sectional shape which comprises extruding a solutioncontaining a'polymer comprised of at least 85% acrylonitrile and up toabout 15% of an ethylenically unsaturated monomer copolymerizable withacrylonitrile in dimethylformamide at a temperature from about 130 C. toabout 145 C. through a spinneret into a first zone of a spinning cellcontaining a substantially solvent-saturated static gaseous medium at atemperature from about 165 C. to about 205 C., passing said filamentswithout cooling into a second zone of said spinning cell whilesimultaneously introducing a fiow from about 20 to about 60 pounds perhour of a solvent-free gaseous medium at a temperature from about 50 C.to about 100 C. in said second zone, and subsequently removing saidfilaments from said second zone at a rate from about 275 to about 350yards per minute.

4. The process of claim 3 in which the flow of said solvent-free gaseousmedium is counter-current to the direction of travel of the filaments.

5. A process for preparing acrylonitrile filaments having a uniform,round cross-sectional shape which comprises extruding a solutioncontaining a polymer comprised of at least acrylonitrile and from about2% to about 15% of a copolymerizable ethylenically unsaturated monomerin dimethylformamide' at a temperature from about 130 C. to about 145 C.and Withdrawing said filaments at a rate from about275 to about 350yards per minute through a spinneret into an atmos phere containing asubstantially solvent-saturated static gaseous medium heated to atemperature from about 165 C. to about 205 C., and thereafter passingsaid filaments through an atmosphere containing a substantiallysolvent-free gaseous medium heated to a temperature from, about 50 C. toabout C. and withdrawing said filaments at a. rate from about 275 toabout 350 yards per minute.

6. A process for preparing acrylonitrile filaments having a uniform,round cross-sectional shape which comprises extruding a solutioncontaining a polymer comprised of at least 85 acrylonitrile, from about2% to about 15% of a copolymerizable ethylenically unsaturated monomer,and from about 0.1% to about 10% of a eopolymerizable sulfonate monomerin dimethylformamide at a temperature from about C. to about C. througha spinneret into an atmosphere contain ing a substantiallysolvent-saturated static gaseous medium heated to a temperature fromabout C. to about 205 C., and thereafter passing said filaments throughan atmosphere containing a substantially solvent-free gaseous mediumheated to a temperature from about 50 C. to about 100 C. and withdrawingsaid filaments at a rate from about 275 to about 350 yards .per minute.

References Cited in the file of this patent UNITED STATES PATENTS2,068,538 Dreyfus et al. Jan. 19, 1937 2,341,615 Hoifman Feb. 15, 19442,761,754 Jones Sept. 4, 1956 2,811,409 Clapp et a1. Oct. 29, 1957UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No,2,975,022 March 14, 1961 Robert D. Euler It is hereby certified thaterror appears in the above numbered patent requiring correction and thatthe said Letters Patent. should read as corrected below.

Column 6, lines 4, 5 and 6 strike out "and withdrawing sald fllaments ata rate from about 275 to about 350 yards per minute".

Signed and sealed this 26th day of December 1961,,

( SEA L). Attest:

ERNEST W. SWIDER DAVID L. LADD Attesting Officer Commissioner of PatentsUSCOMM-DC-

1. A PROCESS FOR PREPARING ACRYLONITRILE FILAMENTS HAVING A UNIFORM,ROUND CROSS-SECTIONAL SHAPE WHICH COMPRISES EXTRUDING A SOULTIONCONTAINING A POLYMER COMPRISED OF AT LEAST 85% ACRYLONITRILE AND UP TOABOUT 15% OF AN ETHYLENICALLY INSATURATED MONOMER COPOLYMERIZABLE WITHACRYLONITRILE IN DIMETHYLFORMAMIDE AT A TEMPERATURE FROM ABOUT 130*C. TOABOUT 145*C. THROUGH A SPINNERET INTO AN ATMOSPHERE CONTAINING ASUBSTANTIALLY SOLVENTSATURATED STATIC GASEOUS MEDIUM HEATED TO ATEMPERATURE